As an optical disk including a plurality of recording layers, a guide layer integration type disk in which a recording layer and a guide layer are formed on the same layer as shown in FIG. 1(a) and a guide layer separation type disk in which a recording layer and a guide layer are separately formed as shown in FIG. 1(b) are known. In the guide layer, a servo signal including position (address) information is recorded as a guide track. In the guide layer integration type disk, even in a non-recorded portion in which information about the recording layer is not recorded, tracking control is possible using the guide track which is integrally formed with the recording layer such that information is recorded on a predetermined track by the guide track. In addition, there is an advantage that information may be recorded and reproduced using a single laser beam.
The guide layer separation type disk requires a laser beam for servo for reading a guide track from the guide layer and a laser beam for recording/reproduction for writing information or reading recorded information on or from the recording layer. When information is recorded on one recording layer, the laser beam for recording/reproduction is condensed on one recording layer while a focal point position of the laser beam for servo moves on the guide track of the guide layer by tracking control, thereby writing information (see Japanese Laid-open Patent Applications No. 2004-241088 and No. 2001-52374). Since the guide layer separation type disk has a simple structure in which the recording layers are laminated, it is possible to easily manufacture the disk. In addition, since multiple recording layers can be more easily formed as compared to the guide layer integration type disk, recording density can be increased.